This invention relates to a device for restraining the upward movement of a dock and particularly relates to a hydraulically assisted restraint device. This invention also relates to an assembly for holding a dock relative a vehicle as well as a method of holding down a spring loaded dock having a pivotal end and a moveable distal end.
Dock levellers generally comprise hinged ramp structures which are disposed in vehicle loading docks to provide a ramp extending between a vehicle load bed and the loading dock to facilitate movement of cargo between the dock and the vehicle and to overcome any difference in elevation between the floor of the vehicle load bed and the dock.
Various structures and devices have heretofore been manufactured and sold some of which include extension lip members. Each of the devices and assemblies in the prior art are subjected to the change in height of the vehicle load bed relative the dock during loading and unloading operations.
Generally speaking the dock has a hinged or pivotal end and a moveable distal end which can move vertically relative to the vehicle""s load bed. Accordingly as the loaded vehicle is backed up towards the dock the distal end is adjusted so as to rest generally at the edge of the load bed of the vehicle. The suspension system of a vehicle is generally compressed due to the weight of the cargo when initially adjusting the dock relative to the load bed. Upon unloading of the cargo, whether by pallet truck or otherwise the weight of the cargo diminishes and the potential energy of the suspension system in the vehicle increases since the weight of the cargo is no longer there to balance the force in the suspension system which generally includes springs. Accordingly such dock levelling devices and apparatus are subject to rapid wear and unwanted damage as a result of this type of movement.
Various devices have heretofore been devised. For example, U.S. Pat. No. 6,327,733 B1 relates to a pit type dock leveller having a frame adapted to be fixedly mounted at a dock with a deck, pivotally mounted to the frame at one end thereof, and having a pivotal lip at the other end. A spring is mounted to the deck and the frame to support and raise the deck. A hydraulic actuator is coupled to the deck and to a pivotal link member that is mounted to the frame. In a powered mode, the hydraulic unit acts as a power assist for the springs to move the deck from a generally horizontal stored position to an operative position. Such device positions the dock by use of an electric hydraulic power utilizing the hydraulic cylinder to move the dock up.
Moreover U.S. Pat. No. 6,163,913 discloses a dock leveller including a pivotal mounted ramp and a lip member pivotally mounted to the distal end of the ramp and moveable between an extended position and a depending position for forming a path between a loading dock and a load bed of a vehicle. A motor operated linear power screw type actuator is connected to the ramp for moving the ramp to an elevated position and includes an extension member which is engageable with a second tube and telescope relationship in such a way that the actuator tube may be controlled after positioning the ramp to engage the load bed of a vehicle so that the actuator is not subject to forces exerted by the ramp during oscillatory movement while the vehicle is being loaded or unloaded. This device generally describes a hydraulic cylinder used to hold up the dock and protect the dock from sudden downward movements.
Moreover U.S. Pat. No. 5,832,554 relates to a dock leveller typically powered by electric actuator or other motive source having a frame and a deck pivotally mounted to the frame.
Furthermore U.S. Pat. No. 5,856,355 relates to a safety device for a vertically stored dock leveller. Electric power is required to allow the dock leveller to be lowered and the dock leveller will stop if electrical power to the control circuit is interrupted.
Furthermore U.S. Pat. No. 5,526,545 also relates to a dock moveable by hydraulic cylinder which mechanism returns a loading dock into a stored position automatically.
These and other devices illustrate the use of devices which hold up docks. There have also been mechanical devices such as wheel style pulley systems which hold docks downwardly as well as mechanical rachet type hold down systems, which can come apart if subjected to increased upward pressure due to unloading of a vehicle.
It is an object of this invention to provide an improved hydraulic hold down system.
It is an object of this invention to provide an improved device for restraining the upward movement of a dock and particularly an assembly for holding a dock relative a vehicle.
It is an aspect of this invention to provide a device for restraining the upward movement of a dock comprising a hydraulic cylinder having a fixed end; a piston slideably disposed in said cylinder so as to define opposed first and second chambers; a rod having one end connected to said slideable piston, extending through said first chamber and having another end adapted for connection to said dock; hydraulic reservoir containing hydraulic fluid communicating with said first chamber; valve means disposed between said reservoir and said first chamber, said valve means having open position permitting said hydraulic fluid to flow from said first chamber to said reservoir and extending said rod in response to said upward movement of said dock; a closed position stopping the flow of said hydraulic fluid from said first chamber to said reservoir and restraining the upward movement of said dock.
It is a further aspect of this invention to provide an assembly for holding a dock relative a vehicle comprising a dock having one end moveable relative said vehicle; means for urging said one end of said dock upwardly relative said vehicle; a hydraulic cylinder having a fixed end relative said dock; a piston slideably disposed in said cylinder so as to define opposed first and second chambers; a rod having one end connected to said slideable piston extending through said first chamber and having another end connected to said moveable dock; hydraulic reservoir containing hydraulic fluid communicating with said first chamber; valve means disposed between said reservoir and said first chamber having an open position permitting said hydraulic fluid to flow from said first chamber to said reservoir so as to extend said rod in response to said upward movement of said dock; a closed position stopping the flow of said hydraulic fluid from said first chamber to said reservoir and restraining said urging means from urging said upward movement of said one end of said dock; means for moving said valve means between said open and closed positions.
It is yet another aspect of this invention to provide a method of holding down a spring loaded dock having a pivotable end and a distal end with a hydraulic cylinder having a valve and a piston slideably disposed in said cylinder so as to define opposed first and second chambers, and a rod having one end connected to said piston, said rod extending through said first chamber and having another end extending outwardly of said first cylinder and connected to said dock comprising the steps of fixing one end of said cylinder relative said dock; connecting said another end of said rod to said dock; opening said valve so as to extend said rod as said spring loaded dock rises; closing said valve to lock said rod in said position and hold said spring loaded dock.